In mining operations, the efficient fragmentation and breaking of rock by means of explosive charges demands considerable skill and expertise. In most mining operations explosive charges are planted in appropriate quantities at predetermined positions within the rock. The explosive charges are then actuated via detonators having predetermined time delays, thereby providing a desired pattern of blasting and rock fragmentation. Traditionally, signals are transmitted to the detonators from an associated blasting machine via non-electric systems employing low energy detonating cord (LEDC) or shock tube. Electric detonators have also been used with some success. Electric detonators are typically attached to a harness wire, and actuate upon receipt of a simple electrical signal. Alternatively, electrical wires may be used to transmit more sophisticated signals to and from electronic detonators. For example, such signaling may include ARM, DISARM, and delay time instructions for remote programming of the detonator firing sequence. Moreover, as a security feature, detonators may store firing codes and respond to ARM and FIRE signals only upon receipt of matching firing codes from the blasting machine. Electronic detonators can be programmed with time delays with an accuracy of 1 ms or less.
The establishment of a wired blasting arrangement involves the correct positioning of explosive charges within boreholes in the rock, and the proper connection of wires between an associated blasting machine and the detonators. The process is often labour intensive and highly dependent upon the accuracy and conscientiousness of the blast operator. Importantly, the blast operator must ensure that the detonators are in proper signal transmission relationship with a blasting machine, in such a manner that the blasting machine at least can transmit command signals to control each detonator, and in turn actuate each explosive charge. Improper physical connections between components of the blasting arrangement can lead to loss of communication between blasting machines and detonators, with inevitable safety concerns. Significant care is required to ensure that the wires run between the detonators and an associated blasting machine without disruption, snagging, damage or other interference that could prevent proper control and operation of each detonator via the attached blasting machine.
Wireless detonator systems offer the potential for circumventing these problems, thereby improving safety and/or operational efficiency at the blast site. By avoiding the use of physical connections (e.g. electrical wires, shock tubes, SEDC, or optical cables) between detonators, and other components at the blast site (e.g. blasting machines) the possibility of improper set-up of the blasting arrangement is reduced. Wireless detonators and corresponding wireless detonator systems are also more amenable to application with automated mining operations, with robotic set-up of detonators and associated explosives in the field, since wireless detonators are not burdened by the complexities of ‘tieing-in’ to harness lines at the blast site.
However, the development of wireless blasting systems presents formidable technical challenges with regard to safety. For example, in direct contrast to traditional electronic detonators that are “powered-up” to receive command signals only once attached to a harness wire at the blast site, wireless detonators must each comprise their own independent or internal power supply (an “operating power supply”) sufficient to power means for receiving, processing, and optionally transmitting wireless signals at the blast site. The mere presence of this operating power supply itself presents an inherent risk of inadvertent actuation for wireless detonators. For example, accidental or inappropriate application of the operating electrical power to the firing circuitry during transportation and storage could result in unintentional detonator actuation. Furthermore, since wireless detonators are ‘continuously’ powered they are at risk of receiving or acting upon inappropriate or spurious command signals at the blast site, even in locations prior to their placement at the blast site. Thus, there remains a great need in the art to improve the safety of blasting systems that employ electronic detonators, and in particular wireless systems.